The specific aim of this study is to prospectively study a non-diseased sibling population of previously diagnosed juvenile periodontitis patients. Cross sectional studies to date (Newman and Socransky, l977; Slots, l976) have related a number of bacterial species suspected of relating to localized juvenile periodontitis. These organisms are now known to include Capnocytophaga ochracea, C. sputigena, C. gingivalis, Actinobacillus actinomycetemcomitans, Eubacterium saburreum and Bacteroides Asaccharolyticus (Tanner, et. al., l979). In addition recent immunologic data (Ebersole, et. al., l980, Genco, et. al., l980) have demonstrated an immunologic response to Actinobacillus actinomycetemcomitans and Bacteroides asaccharolyticus within a juvenile periodontitis group. Utilizing an available periodontosis population, a prospective study design is presented in which a total of eighteen patients will be studied over the course of three years. Documentation will include repeat microbial sampling and multiple clinical indices. The long term objective is to test the hypothesis that increases in a microorganisms number or percentage coincides or precedes periodontal destruction. By following a population at risk, as periodontosis siblings appear to be (Saxen l980), evidence should be available to confirm or disprove the above hypothesis.